1. Field of the Invention
This invention relates to four-point systems and the ability to automatically change testing probe heads in-between two sample tests if a different probe head is required for the next test to be performed.
2. Description of the Background Art
Four-point probe systems are commonly used in device fabrications for monitoring processes such as metal film deposition and ion implantation. This is performed by measuring sheet resistivities of a test wafer processed with the wafer on which micro-devices are being manufactured for comparison to expected sheet resistivities. In the semiconductor industry if a first test was performed on a wafer with a metal film, and the next test to be performed is on ion-implanted wafer, it usually is necessary to change the probe head to get the best measurement results and avoiding cross contamination.
Up to now, changing of probe heads has been done manually for all four-point probe systems. Even in a fully automatic cassette-to-cassette system, there is only one probe head is installed in the system, and there is no provision for automatically changing that single probe head as the types of tests that need to be performed vary. There too that probe head must be changed manually. Changing probe heads is not only time consuming, but also makes it easy to introduce contaminating particles into the system""s mini-environment. Furthermore, mistakes may also happen in changing the probe heads. The present invention overcomes each of these short comings of the prior art.
The present invention provides a test head system and method that permits the automatic interchange of a plurality of tooling as desired to perform various functions on a sample. The test head system of the present invention includes a frame with a base and a panel extending upward from the base. Mounted on the base is a fixed track that defines a travel path along which a carriage is supported and moved, the carriage in turn having a chuck rotationally mounted to support the sample. Additionally there is a rotational mechanism coupled to the chuck and carriage to position the chuck to a desired rotational position, and a drive mechanism attached to the carriage to move the carriage to a desired position along the fixed track. Also included is a plurality of tooling assemblies each affixed to the panel in a position relative to the fixed track to provide a tool opposite any point on the sample as the chuck is advanced and rotated to a position opposite any of the tooling assemblies. Note that the rotational and drive mechanisms are powered in conjunction with each other to position a desired point on the sample beneath a desired one of the tooling assemblies.
In the method of the present invention is provided to test a sample with a plurality of tools with each tool mounted in a separate tooling assembly and the sample to be tested mounted on a rotationally mounted chuck. The method is performed by defining a path in a plane along which the chuck is to be transported and positioning a plurality of tooling assemblies along that path, with each tooling assembly being positioned in a same attitude with respect to, and at a same distance from, the path, then the method includes transporting the chuck along the path to a position adjacent one of the tooling assemblies and rotating the chuck, if necessary, to position a point of interest on the sample immediately adjacent the tool of one of the tooling assemblies. Once positioned, the method proceeds with engaging the tool adjacent the sample with the sample and performing a test on the sample with the engaged tool. Following the testing the method proceeds with disengaging the tool from the sample and repeating the transporting, rotating, engaging, testing and disengaging steps as necessary for each additional test to be performed on the sample.
Thus, the apparatus and method of the present invention enables the sample on the chuck to be tested by any of the tools in the system at any site on the surface of the sample through transporting and rotating the chuck to a position adjacent the needed tool for the test at hand. Therefore, automatic changing of the tool among those installed in the system can be performed seamlessly saving valuable time and resources during production of various items. Notice that the sample-under-test can be changed by a robot in a larger system when the chuck is at a position along the defined path that is not located beneath a tool assembly.